Doped-carbon composites, synthesizing methods and applications of the same

ABSTRACT

A method of synthesizing a doped carbon composite includes preparing a solution having a carbon source material and a heteroatom containing additive, evaporating the solution to yield a plurality of powders, and subjecting the plurality of powders to a heat treatment for a duration of time effective to produce the doped carbon composite.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a divisional application of, and claims benefit ofU.S. patent application Ser. No. 13/767,076, filed Feb. 14, 2013,entitled “DOPED-CARBON COMPOSITES, SYNTHESIZING METHODS AND APPLICATIONSOF THE SAME”, by Tito Viswanathan, now allowed, which is incorporatedherein by reference in its entirety.

Some references, which may include patents, patent applications, andvarious publications, are cited and discussed in the description of thisinvention. The citation and/or discussion of such references is providedmerely to clarify the description of the invention and is not anadmission that any such reference is “prior art” to the inventiondescribed herein. All references cited and discussed in thisspecification are incorporated herein by reference in their entiretiesand to the same extent as if each reference was individuallyincorporated by reference. In terms of notation, hereinafter, “[n]”represents the nth reference cited in the reference list. For example,[1] represents the 1st reference cited in the reference list, namely,Non-covalent doping of graphitic carbon nitride with graphene:controlled electronic structure and enhanced optoelectronic conversionby Y. Zhang, T. Mori, L. Niu and J. Ye, Energy Environ. Sci. 2011, 4,4517.

STATEMENT AS TO RIGHTS UNDER FEDERALLY-SPONSORED RESEARCH

This invention was made with government support under DE-FG36-06G086072awarded by the Department of Energy. The government has certain rightsin the invention.

FIELD OF THE INVENTION

The invention generally relates to carbon materials, and moreparticularly, to doped carbon composites, synthesizing methods andapplications of the same.

BACKGROUND OF THE INVENTION

Traditionally, the materials that have been used in photocatalysis havebeen metal containing, where the metal includes one or more transitionmetals including copper, platinum, indium, gallium, arsenic etc. andsuffer drawbacks such as metal instability in different oxidationstates, cost, toxicity and difficulty associated with the manufacture ofthese materials. Recent work in Germany and China by Antonetti andco-workers [1] shows that metal-free polycarbon nitride can be used inphotocatalytic reaction mentioned above due to the favorable band gapassociated with optical absorption, a value which is about 2.7 eV and isstrategically placed in an energy scale that is efficient in degradationof organic molecules under visible light. However, the efficiency withwhich the degradation takes place is low and not practical due to thevery low amount of light absorbed above 420 nm. Since most of thevisible spectrum lies above that value (up to 800 nm) the quantum yieldand efficiency of the catalytic process is very low.

It would be desirable to shift the onset of visible light absorption tohigher values so that more of the visible light is absorbed which maytranslate to a more efficient photocatalysis for organic moleculedegradation as well as photocatalytic splitting of water. Besides theband gap the positions of the valence band and the conduction band isimportant. The band gap required for splitting water is greater than1.23 eV (less than 1000 nm). However in case of visible light a band gapof less than 3.0 eV (greater than 400 nm) is required. The band gapshould be preferably between 2.43 eV and 3.3 eV. Both the reduction andoxidation potential of water should lie within the band gap of thephotocatalytic material. The energy of the valence band has to be lowerthan the oxidation potential of oxygen in order to generate oxygen,while the energy of the conduction band has to be higher than thereduction potential of hydrogen. When light interacts with the surfaceof the photocatalyst charge separation into excited photons and holesare created which correspond to conduction and valence bandsrespectively. Recombination of these must be avoided for higherefficiency devices and practical applications. Electron mobility to thesurface may be desirable to keep the charges separated.

To achieve the above stated desired properties researchers haveincorporated graphite or graphene in the mixture by preparing carbonnitride in the presence of graphite sheets. The procedure involved thepreparation of a melamine-graphite immiscible mix which was then heatedto a temperature of 550° C. in the presence of nitrogen gas till themelamine molecules condensed to carbon nitride. The product was shown tobe a layered structure comprising of carbon nitride and graphene. Thecomposite was shown to be superior than graphitic carbon nitride (i.e.,carbon nitride that exists in a 2D form similar to graphite). Thus thecomposite made of alternating layers of pristine graphitic carbonnitride and pristine graphite exhibited better photocatalyticdegradation properties than pristine graphitic carbon nitride alone.

However, the use of pre-made graphite in the above-mentioned processadds more time, cost and complexity because it adds to the stepsrequired preparing the material. Furthermore, the preparation usingpremade graphite yields a composite consisting of carbon nitride andgraphite/graphene that are not covalently linked to each other, which isnot desirable.

Therefore, a heretofore unaddressed need exists in the art to addressthe aforementioned deficiencies and inadequacies.

SUMMARY OF THE INVENTION

Accordingly, among other things, it is desirable to invent a process ofpreparing a material with the desired catalytic properties such as highvisible light absorption, stability and ease of synthesis which issuperior to those up to date. It would be preferable to make a materialthat uses renewable resource material during the course of the synthesisand during which the carbon is a covalently incorporated integral partof the final material. The material should exhibit high efficiency forphotocatalytic processes described above. Also the process should beeasy, which does not involve the use of inert or other kind of gasesduring the transformation. Also the process should be quick and not timeconsuming as the state of the art processes upto now involve.

In one aspect, the invention provides such a novel process for thesynthesis of a novel material that can be termed as doped carbon thatexhibits unique spectral properties and is different than any reportedin the literature so far. The process for the material synthesis, amongother things, has the following advantages over the existingtechnologies: (a) it includes renewable resource materials as carbonsource (b) it is very inexpensive, as it uses inexpensive and readilyavailable ingredients; (c) it is quick; (d) it is reproducible; and (e)it does not use any gases from an outside source during the synthesis.

Furthermore, the product made by the process, doped carbon, unlike purecarbon, can impart desirable properties such as increased conductivity,thermal stability and interesting optical properties which could bebeneficial in several applications such as traditional catalysis andphotocatalysis including photocatalytic degradation of organic moleculesin water as well as air. They may also be useful in photocatalyticsplitting of water to produce hydrogen and oxygen under the rightconditions.

In another aspect of the invention, a method of synthesizing a dopedcarbon composite includes the steps of preparing a solution having amaterial containing tannin and an additive containing a doping chemicalelement; evaporating the solution to yield a plurality of powders; andsubjecting the plurality of powders to a heat treatment for a durationof time effective to produce the doped carbon composite.

In one embodiment, the material containing the tannin is tanninsulfonate, lignin, lignosulfonate, or a mixture thereof. The additivecontaining the doping chemical element is one containing oxygen (O),nitrogen (N), phosphorus (P), boron (B), sulfur (S), iodine (I),fluorine (F), silicon (Si), selenium (Se), germanium (Ge), or a mixturethereof.

In one embodiment, the heat treatment is performed at a temperature in arange of about 700° C. to about 1800° C. The duration of time effectiveis in a range of about 10 minutes to about 2 hours.

In one embodiment, the heat treatment is performed by subjecting theplurality of powders to a microwave radiation with a frequency of 2.45GHz.

In another embodiment, the heat treatment is performed by a heat sourceother than a microwave radiation source.

Furthermore, the method may include the step of adding polyphosphoricacid to the plurality of powders prior to the subjecting step.

In yet another aspect of the invention, a composite synthesized bypyrolysis of a mixture of tannin and melamine, where the steps involvedin the synthesis process include dissolving the tannin and the melaminein water to form a homogeneous solution; evaporating the solution toyield a dry solid; and subjecting powders of the dry solid to a heattreatment between about 700° C. and about 1800° C. for about 10 minutesto about 2 hours. Additionally, the synthesis process further may alsohave the step of adding polyphosphoric acid to the plurality of powdersprior to the subjecting step.

In a further aspect of the invention, a method of synthesizing a dopedcarbon composite includes the steps of preparing a solution having acarbon source material and a heteroatom containing additive; evaporatingthe solution to yield a plurality of powders; and subjecting theplurality of powders to a heat treatment for a duration of timeeffective to produce the doped carbon composite.

In one embodiment, the carbon source material comprises tannin, urea,lignin, lignosulfonate, tannin sulfonate, phenol formaldehyde resins,melamine formaldehyde resins, tannin formaldehyde resins, resorcinolformaldehyde resins, urea formaldehyde resins, or a mixture thereof.

In one embodiment, the heteroatom containing additive comprises onecontaining O, N, P, B, S, I, F, Si, Se, Ge, or a mixture thereof.

In one embodiment, the heat treatment is performed at a temperature in arange of about 700° C. to about 1800° C. In one embodiment, the durationof time effective is in a range of about 10 minutes to about 2 hours.

In one embodiment, the heat treatment is performed by subjecting theplurality of powders to a microwave radiation with a frequency of 2.45GHz.

In another embodiment, the heat treatment is performed by a heat sourceother than a microwave radiation source.

In one embodiment, the method also includes the step of addingpolyphosphoric acid to the plurality of powders prior to the subjectingstep.

In yet a further aspect of the invention, a composite synthesized by thesteps of preparing a solution having a carbon source material and aheteroatom containing additive; evaporating the solution to yield aplurality of powders; and subjecting the plurality of powders to a heattreatment for a duration of time effective to produce a doped carboncomposite. In one embodiment, the synthesis process further includes thestep of adding polyphosphoric acid to the plurality of powders prior tothe subjecting step.

In one embodiment, the carbon source material comprises tannin, urea,lignin, lignosulfonate, tannin sulfonate, phenol formaldehyde resins,melamine formaldehyde resins, tannin formaldehyde resins, resorcinolformaldehyde resins, urea formaldehyde resins, or a mixture thereof.

In one embodiment, the heteroatom containing additive comprises acompound containing O, N, P, B, S, I, F, Si, Se, Ge, or a mixturethereof.

In one embodiment, the additive containing the doping chemical elementcomprises a boron compound containing boric acid, or sodium borate.

In one embodiment, the additive containing the doping chemical elementcomprises a phosphorus compound containing phosphoric acid,polyphosphoric acid, or sodium phosphate.

In one embodiment, the additive containing the doping chemical elementcomprises a silicon compound containing potassium silicate.

In one embodiment, the additive containing the doping chemical elementcomprises a fluorine compound containing ammonium fluoride.

In one embodiment, the additive containing the doping chemical elementcomprises an iodine compound containing sodium iodide, or ammoniumiodide.

In one embodiment, the additive containing the doping chemical elementcomprises a nitrogen compound containing melamine, dicyandiamide, urea,guanidine, or histidine. In one embodiment, the additive containing thedoping chemical element further comprises hexamine.

The composite is useable for visible light degradation of organicmolecules in water.

In one aspect of the invention, an article of manufacture is provided,where the article of manufacture is made according to the method setforth above.

The article of manufacture is a supercapacitor, a fuel cell,photovoltaic cell, a lithium ion battery, an air filter, or a waterfilter.

These and other aspects of the invention will become apparent from thefollowing description of the preferred embodiment taken in conjunctionwith the following drawings, although variations and modificationstherein may be affected without departing from the spirit and scope ofthe novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate one or more embodiments of theinvention and, together with the written description, serve to explainthe principles of the invention. Wherever possible, the same referencenumbers are used throughout the drawings to refer to the same or likeelements of an embodiment.

FIG. 1 shows an infrared spectrum of a doped carbon composite preparedin EXPERIMENT 1 according to one embodiment of the invention.

FIG. 2 shows an infrared spectrum of a doped carbon composite preparedin EXPERIMENT 2 according to one embodiment of the invention.

FIG. 3 shows a Fourier transform infrared spectrum (FTIR) of a dopedcarbon composite prepared in EXPERIMENT 7 according to one embodiment ofthe invention.

FIG. 4 shows survey scans of the PNDC and reduced PNDC according to oneembodiment of the invention: (a) showing the presence of O1s, P2p, N1sand C1s elements in the PNDC, and (b) showing the presence of O1s, N1sand C1s elements in the reduced PNDC.

FIG. 5 shows nitrogen sorption linear isotherms of the PNDC and reducedPNDC composites according to one embodiment of the invention.

FIG. 6 shows Tauc plots of the PNDC and reduced PNDC according to oneembodiment of the invention: (a) showing the direct band gap of the PNDCcomposite calculated using the absorption coefficient, and (b) showingthe direct band gap of the hydrazine reduced PNDC.

FIG. 7 shows SEM images of the PNDC and reduced PNDC according to oneembodiment of the invention: (a) showing the spherical morphology of thePNDC along with the graphite like flakes, where inset shows thecross-section of some PNDC spheres, and (b) showing the formation of thePNDC spheres from tannin-melamine-hexamine polymer matrix aftercarbonizing for 10 minutes, where inset demonstrating the growth patternof the spheres inside the polymer matrix.

FIG. 8 shows Raman spectrum of the PNDC, showing D-band and G-band,where inset shows the Raman spectrum of the reduced PNDC according toone embodiment of the invention.

FIG. 9 shows UV-Visible absorption spectra of the PNDC and reduced PNDCaccording to one embodiment of the invention.

FIG. 10 shows cyclic voltammograms of the PNDC and reduced PNDC inoxygen saturated 0.1M KOH solution according to one embodiment of theinvention.

FIG. 11 shows cyclic voltammetry plots of PNDCs in 6.0 M KOH electrolyterecorded (a) at 5 mV, showing the capacitance, and (b) the interfacialcapacitance according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likereference numerals refer to like elements throughout.

The terms used in this specification generally have their ordinarymeanings in the art, within the context of the invention, and in thespecific context where each term is used. Certain terms that are used todescribe the invention are discussed below, or elsewhere in thespecification, to provide additional guidance to the practitionerregarding the description of the invention. For convenience, certainterms may be highlighted, for example using italics and/or quotationmarks. The use of highlighting has no influence on the scope and meaningof a term; the scope and meaning of a term is the same, in the samecontext, whether or not it is highlighted. It will be appreciated thatsame thing can be said in more than one way. Consequently, alternativelanguage and synonyms may be used for any one or more of the termsdiscussed herein, nor is any special significance to be placed uponwhether or not a term is elaborated or discussed herein. Synonyms forcertain terms are provided. A recital of one or more synonyms does notexclude the use of other synonyms. The use of examples anywhere in thisspecification including examples of any terms discussed herein isillustrative only, and in no way limits the scope and meaning of theinvention or of any exemplified term. Likewise, the invention is notlimited to various embodiments given in this specification.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present. As used herein, the term “and/or” includesany and all combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another element, component, region, layer or section. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of the invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising”, or “includes” and/or “including” or “has” and/or“having” when used in this specification, specify the presence of statedfeatures, regions, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, regions, integers, steps, operations, elements,components, and/or groups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top”, may be used herein to describe one element's relationship toanother element as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower”, can therefore, encompasses both an orientation of “lower” and“upper”, depending of the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and theinvention, and will not be interpreted in an idealized or overly formalsense unless expressly so defined herein.

As used herein, “around”, “about” or “approximately” shall generallymean within 20 percent, preferably within 10 percent, and morepreferably within 5 percent of a given value or range. Numericalquantities given herein are approximate, meaning that the term “around”,“about” or “approximately” can be inferred if not expressly stated.

As used herein, if any, the term “scanning electron microscope” or itsabbreviation “SEM” refers to a type of electron microscope that imagesthe sample surface by scanning it with a high-energy beam of electronsin a raster scan pattern. The electrons interact with the atoms thatmake up the sample producing signals that contain information about thesample's surface topography, composition and other properties such aselectrical conductivity.

As used herein, if any, the term “X-ray photoelectron spectroscopy” orits abbreviation “XPS” refers to a method used to determine thecomposition of the top few nanometers of a surface. It involvesirradiating a material with a beam of X-rays while simultaneouslymeasuring the kinetic energy and number of electrons that escape fromthe top 1 to 10 nm of the material being analyzed.

As used herein, the terms “comprising,” “including,” “having,”“containing,” “involving,” and the like are to be understood to beopen-ended, i.e., to mean including but not limited to.

The description will be made as to the embodiments of the invention inconjunction with the accompanying drawings in FIGS. 1-11. In accordancewith various embodiments of the invention, as embodied and broadlydescribed herein, this disclosure, in one aspect, relates to dopedcarbon composites exhibiting unique properties and being different thanany reported in the literature so far, and a synthesizing process of thesame.

According to the invention, the synthesizing process is a novelimprovement over U.S. Pat. No. 8,167,973, entitled “MICROWAVE-ASSISTEDSYNTHESIS OF CARBON AND CARBON-METAL COMPOSITES FROM LIGNIN, TANNIN ANDASPHALT DERIVATIVES”, U.S. patent application Ser. No. 12/487,323,entitled “MICROWAVE-ASSISTED SYNTHESIS OF CARBON AND CARBON-METALCOMPOSITES FROM LIGNIN, TANNIN AND ASPHALT DERIVATIVES AND APPLICATIONSOF SAME”, and U.S. patent application Ser. No. 13/335,418, entitled“RENEWABLE RESOURCE-BASED METAL-CONTAINING MATERIALS AND APPLICATIONS OFTHE SAME”, which are incorporated herein by reference in theirentireties.

According to various embodiments of the invention, doped carboncomposites/materials are synthesized/made by adding heteroatomcontaining compounds to canon sources including tannin, lignin andderivatives, and pyrolyzing the mixture such that the carbon producedcontains the heteroatom in the molecular structure in varying amountsdepending on the ratio of the carbon to the heteroatom in the precursor.In one embodiment, the heteroatom includes nitrogen and phosphorus.However, other heteroatom can also be used to practice the invention.

The novel doped carbon componds/materials contain nitrogen and carbon,as well as nitrogen, carbon and phosphorus. In one embodiment, the dopedcarbon composite is made by the carbonization of tannin in the presenceof melamine. The process is modifiable by using different carbon sourcessuch as urea, lignin, lignosulfonate, tannin sulfonate, phenolformaldehyde resins, melamine formaldehyde resins, tannin formaldehyderesins, resorcinol formaldehyde resins and urea formaldehyde resins. Inaddition, other renewable and non-renewable resource materials thatcontain carbon can also be used. Examples include sucrose, lactose, andglucose as renewable resource materials and polystyrene,naphthalenesulfonate as non-renewable resource based materials.Heteroatom containing compounds with oxygen (O), nitrogen (N),phosphorus (P), boron (B), sulfur (S), iodine (I), flourine (F), silicon(Si), selenium (Se), germanium (Ge) and mixtures thereof can be used toproduce the appropriately doped carbon material. Furthermore, theprocess is carried out in an ambient atmosphere, i.e., the absence ofany inert or reducing gases.

In one aspect of the invention, the synthesizing process of a dopedcarbon composite includes the steps of preparing a solution having amaterial containing tannin and an additive containing a doping chemicalelement; evaporating the solution to yield a plurality of powders; andsubjecting the plurality of powders to a heat treatment for a durationof time effective to produce the doped carbon composite. In addition,the method may also include the step of adding polyphosphoric acid tothe plurality of powders prior to the subjecting step.

The material containing the tannin can be tannin sulfonate, lignin,lignosulfonate, or a mixture thereof. The additive containing the dopingchemical element can be one containing O, N, P, B, S, I, F, Si, Se, Ge,or a mixture thereof.

In one embodiment, the heat treatment is performed, for example, in anoven, a muffle furnace or the like, at a temperature in a range of about700° C. to about 1800° C. The duration of time effective is in a rangeof about 10 minutes to about 2 hours.

In another embodiment, the heat treatment is performed by subjecting theplurality of powders to a microwave radiation, for example, with afrequency of 2.45 GHz at about 1.25 KW power and irradiated for about 30minutes.

In another aspect of the invention, the doped carbon composite issynthesized by the pyrolysis of a mixture of tannin and melamine, wherethe steps involved in the synthesis process include dissolving thetannin and the melamine in water to form a homogeneous solution;evaporating the solution to yield a dry solid; and subjecting powders ofthe dry solid to a heat treatment between about 700° C. and about 1800°C. for about 10 minutes to about 2 hours. Additionally, the synthesisprocess further may also have the step of adding polyphosphoric acid tothe plurality of powders prior to the subjecting step.

In yet another aspect of the invention, a synthesizing process of adoped carbon composite includes the steps of preparing a solution havinga carbon source material and a heteroatom containing additive;evaporating the solution to yield a plurality of powders; and subjectingthe plurality of powders to a heat treatment for a duration of timeeffective to produce the doped carbon composite.

In one embodiment, the carbon source material comprises tannin, urea,lignin, lignosulfonate, tannin sulfonate, phenol formaldehyde resins,melamine formaldehyde resins, tannin formaldehyde resins, resorcinolformaldehyde resins, urea formaldehyde resins, or a mixture thereof.

In one embodiment, the heteroatom containing additive comprises onecontaining or a mixture thereof.

In one embodiment, the heat treatment is performed at a temperature in arange of about 700° C. to about 1800° C. In one embodiment, the durationof time effective is in a range of about 10 minutes to about 2 hours.

In one embodiment, the heat treatment is performed by subjecting theplurality of powders to a microwave radiation with a frequency of 2.45GHz.

In another embodiment, the heat treatment is performed by a heat sourceother than a microwave radiation source.

In yet a further aspect of the invention, a composite synthesized by thesteps of preparing a solution having a carbon source material and aheteroatom containing additive; evaporating the solution to yield aplurality of powders; and subjecting the plurality of powders to a heattreatment for a duration of time effective to produce a doped carboncomposite. In one embodiment, the synthesis process further includes thestep of adding polyphosphoric acid to the plurality of powders prior tothe subjecting step. In one embodiment, the method also includes thestep of adding polyphosphoric acid to the plurality of powders prior tothe subjecting step.

The carbon source material includes tannin, urea, lignin,lignosulfonate, tannin sulfonate, phenol formaldehyde resins, melamineformaldehyde resins, tannin formaldehyde resins, resorcinol formaldehyderesins, urea formaldehyde resins, or a mixture thereof.

The heteroatom containing additive includes a compound containing O, N,P, B, S, I, F, Si, Se, Ge, or a mixture thereof. Without intent to limitthe scope of the invention, the following are examples of the heteroatomcompound. The boron compound contains boric acid, or sodium borate. Thephosphorus compound contains phosphoric acid, polyphosphoric acid, orsodium phosphate. The silicon compound contains potassium silicate. Thefluorine compound contains ammonium fluoride. The iodine compoundcontains sodium iodide, or ammonium iodide. The nitrogen compoundcontains melamine, dicyandiamide, urea, guanidine, or histidine.Further, the additive may also have hexamine.

According to the invention, the doped carbon composite is useable forvisible light degradation of organic molecules in water.

In one aspect of the invention, an article of manufacture is provided,where the article of manufacture is made according to the method setforth above. The article of manufacture is usable in a supercapacitor, afuel cell, a photovoltaic cell, a lithium ion battery, an air filter, awater filter, or the likes.

The salient features associated with the process will be evident afterthe experiments described below.

Without intent to limit the scope of the invention, further exemplaryprocesses and their related results according to the various embodimentsof the invention are given below.

Experiment 1 Microwave Assisted Synthesis of Photoactive Phosphorus (P)and Nitrogen (N) Doped Carbon

About 1.62 g of tannin and about 1.26 g of melamine were dissolved inabout 50 mL of water with a few drops of methanol for added solubility,thereby, forming a mixture thereof. The mixture was heated until thesolutes dissolved and the heating was continued until all the waterevaporated from the evaporating dish. The resulting dry solid wasscraped, which weighed about 2.45 g. Then, about 1 g of the powderedsample was placed in an alumina crucible with about 4 drops ofphosphoric acid and covered with another boron nitride crucible andplaced in a microwave oven operating at about 1.08 kW under ambientconditions for about 10 minutes. The sample was left for about 15minutes to cool and a dark material was obtained and weighed (at about0.438 g). The resulted material appeared dark green under an opticalmicroscope and was electrically conductive when the leads of amultimeter were used to determine conductivity. Infrared spectrum of thephosphorus and nitrogen doped carbon obtained in this experiment isshown in FIG. 1.

Experiment 2 Synthesis of the Photoactive Phosphorus (P) and Nitrogen(N) Doped Material

About 1.62 g of tannin and about 1.26 g of melamine were dissolved inabout 50 mL of water with a few drops of methanol for added solubility,thereby, forming a mixture thereof. The mixture was heated until thesolutes dissolved and the heating was continued until all the waterevaporated from the evaporating dish. The resulting dry solid wasscraped, which weighed about 2.45 g. The dry powdered sample was placedin an alumina crucible and covered with an alumina lid and placed in amuffle furnace at about 900° C. for about 2 hours under ambientconditions. Following the 2 hour period, the muffle furnace was turnedoff and the exhaust hole on the top was covered with a petridish.Cooling was allowed to take place for several hours after which thefurnace was opened and the dark material was obtained and weighed (atabout 0.147 g). The obtained material appeared dark green under anoptical microscope and was electrically conductive when the leads of amultimeter were used to determine conductivity. The infrared spectrum ofthe nitrogen doped carbon material has three prominent absorption bands,as shown in FIG. 2. The peak centered at about 3431 cm⁻¹ is indicativeof O—H stretching. The peak at about 1620 cm⁻¹ is due to C═O stretch.Identity of another prominent peak at about 1445 cm⁻¹ has not beenestablished yet. Some other less prominent peaks appear at about 1051cm⁻¹, about 870 cm⁻¹ and about 565 cm⁻¹, respectively.

Experiment 3 Synthesis of Phosphorus (P) and Silicon (Si) Doped Carbon

An about 0.6 g sample of silicone oil (Pure Silicone Fluid, 500 cSt,from Clearco Products Co., Inc., Bensalem, Pa.) was mixed with about0.62 g of polyphosphoric acid in a born nitride crucible to form amixture. Further, about 2 g of tannin was added to the mixture and mixedwell to make a slurry. The crucible was lightly covered with anotherboron nitride crucible and placed in an alumina foam box covered on allsides. This setup was placed in a microwave oven operating at about 2.45GHz at about 1.25 KW power and irradiated for about 30 minutes. Thecrucible was taken out of the microwave oven after cooling for about anhour and a half. A highly conductive black material that weighed about0.923 g was obtained.

Experiment 4 Degradation of Methylene Blue Dye (MB) by Visible Light

Visible light photocatalytic degradation of methylene blue dye (MB) inwater using light from an overhead projector was demonstrated asfollows:

An about 2 mg sample of MB obtained in EXPERIMENT 2 was dissolved inabout 100 mL of water to form a mixture. About 50 mg of the nanomaterialabove was added in the mixture and the stirred mixture was placed at adistance of about 8 cm from the lamp of an overhead projector that waslit using an about 360 W, 80 V halogen photooptic lamp. The blue colorof the dye disappeared completely to the naked eye in about 40 minutes.Partial discoloration observed in the absence of light reappeared whenmethanol was added. Similar treatment with light treated material didnot yield the color back.

After the initial color disappearance, another 2 mg of the dye was addedand photo treatment was carried out. Complete dye degradation indicatedby complete color loss was evident in about 40 minutes. Following thisprocess, another 4 mg of MB was added and subjected to the sametreatment as above. A similar observation was made after photo treatmentfor about 2 hours.

Experiment 5 Degradation of Methylene Blue Dye (MB) by Visible LightUsing Microwave Made Material

Visible light photocatalytic degradation of methylene blue dye (MB) inwater by material made by the microwave method using light from anoverhead projector was demonstrated as follows:

An about 1.0 mg sample of MB was dissolved in about 50 mL of water toform a mixture. Then, about 25 mg of the nanomaterial obtained inEXPERIMENT 3 was added in the mixture and the stirred mixture was placedin front of an overhead projector that was lit using an about 360 W 80 Vhalogen photooptic lamp. The blue color of the dye disappearedcompletely to the naked eye in about 10 minutes. Partial discolorationobserved in the absence of light reappeared when methanol was added.Similar treatment with light treated material did not yield the bluecolor back.

Experiment 6

An about 4.32 g sample of tannin and about 1.89 g of melamine weredissolved in about 95 mL of hot water at a temperature close to about100° C., to form a solution. Then about 0.69 g of hexamethylenetetramine (HMTA) dissolved in about 5 mL of water was added to thesolution and continued to heat. Heating was continued until all theliquid evaporated, resulting in a dry solid material. The weight of theobtained dry solid material was about 5.95 g.

An about 1 g sample of the dry powdered material obtained from the aboveprocess was placed in a zirconia crucible and covered lightly with asmall boron nitride crucible after the addition of about 3 drops ofconc. nitric acid and about 2 drops of phosphoric acid. It wasmicrowaved for about 30 minutes at about 1.2 kW power. The crucible wascooled and about 4 more drops of phosphoric acid were added, then cappedand microwaved for about another 30 minutes. After cooling, about 0.32 gof a black material was obtained, which was conductive.

About 50 mg of this material was added to a stirred solution containingabout 2.3 mg of methylene blue in about 40 mL water placed in the pathof an about 360 W projector light. The blue color disappeared to thenaked eye in about 25 minutes. Another 1.8 mg of MB added wasdecolorized in about 13 minutes. Further addition of about 1.4 mg ofmethyl violet was decolorized in about 11 minutes. Further addition ofabout 1.9 mg of methyl orange was decolorized in about 15 minutes.

Experiment 7

An about 4.32 g sample of tannin and about 1.89 g of melamine weredissolved in about 95 mL of hot water at a temperature close to 100° C.Then about 0.69 g of hexamethylene tetramine (HMTA) dissolved in about 5mL of water was added to the solution and continued to heat. Heating wascontinued until all the liquid evaporated resulting in a dry solidmaterial. The weight of the obtained dry solid obtained was about 5.95g.

An about 1 g sample of the powdered material obtained from the aboveprocess was placed in a zirconia crucible and covered lightly with asmall boron nitride crucible after the addition of about 2 drops ofpolyphosphoric acid. It was microwaved for about 30 minutes at about 1.2kW power. After cooling, about 0.30 g of the black material wasobtained, which was conductive.

About 50 mg of this material was added to a stirred solution containingabout 1.5 mg of methylene blue in about 50 mL water placed in the pathof an about 360 W projector light. The blue color disappeared to thenaked eye in about 12 minutes. Another 4.2 mg of MB added was completelydecolorized in about 25 minutes.

The Fourier transform Infrared spectrum (FTIR) of the phosphorus andnitrogen doped carbon material obtained in this experiment is shown inFIG. 3.

Further Characterization and Applications

Elemental compositions of the phosphorus and nitrogen doped carbon(PNDC) and hydrazine reduced PNDC compounds are listed in Table 1.

TABLE 1 Elemental composition of PNDC and reduced PNDC compounds.Nitrogen Phosphorus Oxygen Carbon Atomic % (N1s) (P2p) (O1s) (C1s) PNDC1.12 2.98 10.72 85.19 Reduced PNDC 0.95 0.00 5.73 93.08

Upon reduction with hydrazine, the oxygen content in the PNDC wasreduced from about 10.72% to about 5.73% and phosphorus was completelyremoved, as shown in Table 1. The complete loss of phosphorus uponreduction is attributed to the formation of (soluble) ammoniumphosphates that was washed away during filtration. The mechanism of thisis however not quite clear.

X-Ray Photoelectron Spectroscopy (XPS) Characterization:

Doping of carbon by nitrogen and phosphorus established by the existenceof N and P in the XPS survey scans, as shown in FIG. 4, where (a) thesurvey scan of PNDC shows the presence of O1s, P2p, N1s and C1selements, and (b) the survey Scan of reduced PNDC shows the presence ofO1s, N1s and C1s elements.

The deconvoluted N1s spectrum of the PNDC shows the existence of fivedifferent nitrogen configurations, out of which the pyridinic (398.13eV, 17.71 atomic %) and pyrrolic (400.49 eV, 61.77 atomic %) moietiesare the most dominant. Nitrogen exists in five different bindingenergies, pyridinic (398.13 eV), pyrollic (400.49 eV), N-Oxide (403.59eV), one low energy bond at 394.09 eV and high energy bond at 405.95 eV.Two different configurations for phosphorous are also identified fromits deconvoluted P2p spectra, namely, P—O (132.94 eV) and a new highenergy bond at 136.34 eV. The peak assignments for the low and highenergy bonds for nitrogen and the high energy bond for phosphorous hasnot been identified so far. Carbon exhibits five different bindingenergies namely graphitic/sp² carbons (283.98 eV), carbonyl (285.58 eV),adventitious carbon (285.22 eV), C—N—C bond (289.24 eV) and N—C—O(292.98 eV). Deconvoluted O1s spectra show the existence of fivedifferent binding energies namely quinone (529.95 eV), carbonyl (531.79eV), C—O (533.00 eV), C—OH (534.39 eV) and absorbed water (535.99 eV).

BET (Brunauer-Emmett-Teller) Surface Area Analysis:

The PNDC and reduced PNDC have a microporous structure as the nitrogenadsorption isotherms. The BET surface area for the PNDC was about 1000m²/g according to the BET method, while the reduced PNDC has a BETsurface area of about 680 m²/g. FIG. 5 shows nitrogen sorption linearisotherms of the PNDC and reduced PNDC composites.

UV-Visible Spectroscopy:

Bandgaps of the PNDC and reduced PNDC are determined from the absorptioncoefficients values from the UV-Visible absorption spectra using Taucequation. Plots of (ahv)² vs eV are shown in FIG. 6, where (a) is theTauc plot showing the direct band gap of the PNDC composite calculatedusing the absorption coefficient, and (b) is the Tauc plot showing thedirect band gap of the hydrazine reduced PNDC.

Scanning Electron Microscope (SEM) Analysis:

The synthesized PNDC has a dense spherical morphology ranging from about0.5 μm to about 2.6 μm in diameter. A trivial amount of graphite-likeplanes/sheets are also observed. FIG. 7 shows (a) an SEM image showingthe spherical morphology of the PNDC along with the graphite likeflakes. Inset shows the cross-section of some PNDC spheres, and (b) anSEM image showing the formation of the PNDC spheres fromtannin-melamine-hexamine polymer matrix after carbonizing for 10minutes. Inset demonstrates the growth pattern of the spheres inside thepolymer matrix.

Raman Spectroscopy:

The Raman spectrum of the PNDC exhibits two different bands at about1320 cm⁻¹ and about 1588 cm⁻¹, which corresponds to the D-band andG-band of the sp² carbon atoms. The G-band is due to the specificvibrations of carbon atoms in the graphite crystal plane and D-bandarises due to the defects in the graphite crystal plane, as shown inFIG. 8. The Raman spectrum of the reduced PNDC is shown in an inset ofFIG. 8, where the I_(D)/I_(G) value was found to be less than PNDC dueto fewer defects and improved conjugation of sp² carbons atoms.

UV-Visible Spectroscopy:

The PNDC shows broad range of absorption in the UV-Visible spectrum. Themaximum absorbance was found to be about 314 nm, with the onset ofabsorption around about 600-700 nm, while the reduced PNDC exhibits amaximum about 333 nm, as shown in FIG. 9. This red shift upon reductionis attributed to the improved continuous carbon network upon reduction.Upon reduction the oxygen atoms involved in formation of carbonyl, epoxyand hydroxyl bonds are removed. Direct band gaps of the PNDC and reducedPNDC were found to be 2.68 eV and 2.72 eV respectively as analyzed bythe Tauc equation.

Cyclic Voltammetry:

Cyclic voltammograms of the PNDC and reduced PNDC in oxygen saturated,0.1 M KOH are shown in FIG. 10. The oxygen reduction reaction (ORR)potential of the PNDC was found to be at about −0.57 V, with an onsetpotential of −0.23 V. However, in the case of the reduced PNDC, the ORRpotential was found to be at about −0.23 V, with an onset potential atabout 0.18 V. Upon reduction of the PNDC, ORR potential shifted towardsthe positive side. The reduction potential of reduced PNDC is found moretowards the positive voltages when compared to other heteroatom dopedcarbon materials synthesized by different methods. This material is verypromising for ORR applications due to the presence of relatively highamounts of pyridinic and pyrrolic nitrogens.

Supercapacitance:

Supercapacitance evaluation was carried out electrochemically usingthree electrode systems similar to the ORR evaluation (cyclicvoltammogram, as shown in FIG. 11). Capacitance of the compositesfollowed linearity based on amount of nitrogen doping as well as surfacearea. Interfacial capacitance was calculated based on their BET specificsurface area and increased nitrogen content lowered the specific surfacearea (about 113 m²/g) due to loss of micropores showing higherinterfacial capacitance, as shown in FIG. 11(b). The optimum nitrogendoping resulted in high surface area (about 479-855 m²/g) with idealinterfacial capacitance. The highest interfacial capacitance of about1.8 F/m² was observed with PNDC-4 at potential of about −0.78 V vs.Hg/HgO (cathodic branch) which is very high and comparable to the bestliterature values. The cyclic voltammetry plots of the PNDCs in 6.0 MKOH electrolyte are shown in FIG. 11: (a) at 5 mV, showing thecapacitance, and (b) the interfacial capacitance.

Thus, the photoactive doped carbons with efficient ORR and highcapacitance show excellent potential of these renewable resource-basednanostructured materials in photo/electrochemical energy devices, andcould play a significant role in next generation energy devices.

In sum, the invention, among other things, recites a synthesis processof novel materials, termed as doped carbon, which exhibits many uniquespectral properties that are different than any reported in theliterature so far. The synthesis process has at least the followingadvantages over the conventional process: (a) including renewableresource materials as carbon source, (b) being cheap, as it usesinexpensive and readily available ingredients, (c) being quick, (d)being reproducible, and (e) not using any gases from an outside sourceduring the synthesis.

According to the invention, novel materials are made containing nitrogenand carbon as well as nitrogen, carbon and phosphorus. In oneembodiment, the materials are made by the carbonization of tannin in thepresence of melamine. The process can be modified by using differentcarbon sources such as urea, lignin, lignosulfonate, tannin sulfonate,phenol formaldehyde resins, melamine formaldehyde resins, tanninformaldehyde resins, resorcinol formaldehyde resins and ureaformaldehyde resins. In addition, other renewable and non-renewableresource materials that contain carbon may be used. Examples includesucrose, lactose, and glucose as renewable resource materials andpolystyrene, naphthalenesulfonate as non-renewable resource basedmaterials. Heteroatom containing compounds with sulfur, nitrogen,phosphorus, boron, iodine, fluorine, silicon, germanium and mixturesthereof can be used to produce the appropriately doped carbon materials.

Doped carbon unlike pure carbon can impart desirable properties such asincreased conductivity, thermal stability and interesting opticalproperties which can be beneficial in applications such as traditionalcatalysis and photocatalysis including photocatalytic degradation oforganic molecules in water as well as air. They can be useful inphotocatalytic splitting of water to produce hydrogen and oxygen underthe right conditions. They can also be useful in fuel cells,supercapacitors as well as in lithium batteries. Specifically, thematerials produced by various embodiments of this invention can findapplications, but not limited, in the following, areas:

-   -   1. Enhanced decomposition of organic molecules (including fats,        oils, polychlorinated biphenyls, explosives, dyes and organic        toxic runoffs) due to the large surface area and appropriate        bandgap of the novel materials.    -   2. Use the novel materials as anti-bacterial, anti-virus and        anti-fungal applications useful in the food and bio-medical        industries.    -   3. Air purification systems to kill microbes, volatile organic        compounds, formaldehyde, ammonia, cigarette fumes, automobile        and industrial exhausts.    -   4. Water purification systems.    -   5. Destruction of chemical warfare agents.    -   6. Hydrogen production by splitting water and use in fuel cells.    -   7. Self-cleaning surfaces including odor absorbing and odor        destroying properties.    -   8. Destruction of ethylene gas for prolonging the life of        fruits.    -   9. Photovoltaic applications.    -   10. Supercapacitors and batteries including Li batteries.

Many more applications can be found in various areas as well.

The foregoing description of the exemplary embodiments of the inventionhas been presented only for the purposes of illustration and descriptionand is not intended to be exhaustive or to limit the invention to theprecise forms disclosed. Many modifications and variations are possiblein light of the above teaching.

The embodiments were chosen and described in order to explain theprinciples of the invention and their practical application so as toactivate others skilled in the art to utilize the invention and variousembodiments and with various modifications as are suited to theparticular use contemplated. Alternative embodiments will becomeapparent to those skilled in the art to which the invention pertainswithout departing from its spirit and scope. For example, multipleprobes may be utilized at the same time to practice the invention.Accordingly, the scope of the invention is defined by the appendedclaims as well as the foregoing description and the exemplaryembodiments described therein.

REFERENCE LIST

-   [1] Non-covalent doping of graphitic carbon nitride with graphene:    controlled electronic structure and enhanced optoelectronic    conversion by Y. Zhang, T. Mori, L. Niu and J. Ye, Energy Environ.    Sci. 2011, 4, 4517.-   [2] Carbon nitride preparation method, Mamakhel et al US    2010/0015030A1, Jan. 21, 2010.-   [3] Preparation of high nitrogen compound and materials therefrom,    Huynh et al, U.S. Pat. No. 7,119,179 B1, Oct. 10, 2006.

What is claimed is:
 1. A method of synthesizing a doped carboncomposite, comprising the steps of: (a) preparing a solution having amaterial containing tannin and a non-metallic additive containing adoping chemical element; (b) evaporating the solution to yield aplurality of powders; and (c) subjecting the plurality of powders to aheat treatment for a duration of time effective to produce the dopedcarbon composite, wherein no metal source material is used in themethod, such that the doped carbon composite does not contain metalcomponent.
 2. The method of claim 1, wherein the material containing thetannin is tannin sulfonate, lignin, lignosulfonate, or a mixturethereof.
 3. The method of claim 1, wherein the non-metallic additivecontaining the doping chemical element is one containing oxygen (O),nitrogen (N), phosphorus (P), boron (B), sulfur (S), iodine (I),fluorine (F), or a mixture thereof.
 4. The method of claim 1, whereinthe heat treatment is performed at a temperature in a range of about700° C. to about 1800° C.
 5. The method of claim 4, wherein the durationof time effective is in a range of about 10 minutes to about 2 hours. 6.The method of claim 1, wherein the heat treatment is performed bysubjecting the plurality of powders to a microwave radiation with afrequency of 2.45 GHz.
 7. The method of claim 1, wherein the heattreatment is performed by a heat source other than a microwave radiationsource.
 8. The method of claim 1, further comprising the step of addingpolyphosphoric acid to the plurality of powders prior to the subjectingstep.